知識點

子查詢

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數據表

world

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題目內容

1.List each country?name?where the?population?is larger than that of 'Russia'.（查找人口數大于'Russia'的國家）

SELECT name FROM worldWHERE population >(SELECT population FROM worldWHERE name='Russia')

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2.Show the countries in Europe with a per capita GDP greater than 'United Kingdom'.（查找人均GDP大于'United Kingdom'的國家，人均GDP=GDP/人口數）

select name from world where continent = 'Europe' and gdp/population > (select gdp/population from world where name = 'United Kingdom')

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3.List the?name?and?continent?of countries in the continents containing either?Argentina?or?Australia. Order by name of the country.（查找和‘Argentina’或者‘Australia’在同一個洲的國家名稱和洲名稱，按照國家名稱排序）

select name,continent from world where continent in (select continent from world where name in ('Argentina','Australia')) order by name

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4.Which country has a population that is more than Canada but less than Poland? Show the name and the population.（查找人口數多于‘Canada’，但少于‘Poland’的國家名稱和人口數）

ps：這道題不可以用between and，因為題目要求不包含上下限，而between and是包含上下限的

select name,population from world where population > (select population from world where name='Canada') and population <(select population from world where name='Poland') order by name

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5.Show the name and the population of each country in Europe. Show the population as a percentage of the population of Germany.（查找‘Europe’洲中的國家名稱和人口百分比，人口百分比=人口數/‘Germany’國家人口數）

select name, concat(round(population/(select population from world where name = 'Germany')*100,0),'%') from world where continent = 'Europe'

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6.Which countries have a GDP greater than every country in Europe? [Give the?name?only.] (Some countries may have NULL gdp values).（查找GDP大于‘Europe’中每一個國家GDP的國家，需要注意有的國家GDP為0）

select name from world where gdp > all(select gdp from worldwhere continent = 'Europe'and gdp > 0)

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進階練習

7.Find the largest country (by area) in each continent, show the?continent, the?name?and the?area.（查找每個大洲中面積最大的國家的國家名稱、隸屬洲名、面積）

SELECT continent, name, area FROM world xWHERE area >= ALL(SELECT area FROM world yWHERE y.continent=x.continentAND area > 0)

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8.List each continent and the name of the country that comes first alphabetically.（查找每個大洲中按照字母排序排在第一的國家的國家名稱、隸屬洲名）

select continent,name from world x where x.name=(select y.name from world y where y.continent=x.continent order by name limit 1)

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難度挑戰

9.Find the continents where all countries have a population <= 25000000. Then find the names of the countries associated with these continents. Show?name,?continent?and?population.（查找每個國家的人口數都≤25000000的大洲，并查詢這些大洲下的國家名稱、洲名稱、人口數）

select name,continent,population from world x where 25000000 >= all(select population from world ywhere x.continent = y.continentand population > 0)

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10.Some countries have populations more than three times that of any of their neighbours (in the same continent). Give the countries and continents.（查找隸屬同一個洲，且人口數是其他國家人口數3倍的國家名稱、洲名稱）

select name,continent from world x where x.population/3 >= all (select y.population from world ywhere x.continent = y.continentand x.name <> y.nameand population >0)

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總結

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